Log entry type definitions

[ecpeterson]

The function log-entry takes a plist of arguments and retains them, still as a raw plist, for later perusal. This allows us to mimic most of the functionality of structured log entries without the overhead of having to define a bunch of actual structures. This flexibility comes at a significant cost: without a comprehensive list of log entry types and their fields, we are liable to duplicate entry types and misspell fields, so that they are not recallable or only partially recallable by filtering.

It would be preferable to enforce log entry safety by defining such types as using them. Perhaps this is not always desirable, and log-unsafe-entry should also be available for the casual log programmer, but it would be a better default.